Apparatus and process for coating paper



Aug. 4, 1953 R. N. GRIESHEIMER ET AL 7,8 2

APPARATUS AND PROCESS FOR COATING PAPER iled Jan. 5]., 1948 2 Sheets-Sheet l obbbbbb bobbbbb R. N. GRIESHEIMER ETAL 2,647,842

APPARATUS AND PROCESS FOR COATING PAPER Aug. 4, 1953 2' Sheets-Sheet 2 iled Jan. 31, 1948 INVENTOR 51% BY TTORNEY Patented Aug. 4, 1953 APPARATUS AND PROCESS FOR COATING PAPER.

Rudolph N. Griesheimer and Robert C. Hydell,

Chillicothe, Ohio, assignors to The Mead Corporation, Dayton, Ohio, a corporation of Ohio Application January 31, 1948, Serial No. 5,526

14 Claims. 1

This invention relates to the manufacture of paper, and more particularly paper having surface finishing material applied thereto to provide surface characteristics suitable for receiving better quality printing and especially suitable to meet the exacting requirements of printing halftone and multi-color reproductions in magazine illustrations and the like.

One of the objects of this invention is to provide a method of applying coating material to a paper web or sheet to provide a surface adapted for printing which comprises applying the coating material in controlled quantity and distribution per unit area, effecting a smoothing and blending action upon said coating material to give a substantially uniform and smooth surfaced distribution thereof, and modifying the normal characteristics of said coating material while in said blended and smooth surfaced distribution by subjecting said applied coating to a controlled,

low temperature of the order of substantially below freezing.

Another object of this invention is to provide a method of applying coating material to a paper web or sheet to provide a surface adapted for printing which comprises applying the coating material in controlled quantity and distribution per unit area, effecting a smoothing and blending action upon said coating material to give a substantially uniform and smooth surfaced distribution thereof, and modifying the normal characteristics of said coating material while in said blended and smooth surfaced distribution by subjecting said applied coating to a low temperature treatment, controlled to be sufficiently low and of the order of substantially below freezing, to effect stabilizing of said blended and smooth surfaced coating material substantially to prevent adverse disturbance thereof as the coating material passes through and out of the low temperature treatment zone.

Another object of this invention is to provide a method of applying coating material to a paper web or sheet to provide a surface adapted for printing which comprises applying the coating material in controlled quantity and distribution per unit area, effecting a smoothing and blending action upon said coating material to give a substantially uniform and smooth surface distribution thereof, and modifying the normal characteristics of said coating material while in said blended and smooth surfaced distribution by subjecting said applied coating to a controlled low temperature sufficiently low to effect stabilizing of said coating material in said blended and LTI smoothed condition to prevent adverse adhesion between the applied coating material and the surface smoothing and blending member and maintaining said coating material stabilized in said blended and smoothed modified condition while effecting substantially complete separation of said smoothed surface and the smoothing and blending member, and thereafter treating said modified condition coating material to cause reverting from said modified condition and drying thereof without objectionably effecting disturbance of said blended and smoothed surface condition.

Another object of this invention is to provide a method of applying coating material to a paper web or sheet to provide a surface adapted for printing which comprises applying the coating material in controlled quantity and distribution per unit area, effecting a smoothing and blending action upon said coating material to give a substantially uniform and smooth surfaced distribution thereof, and modifying the normal characteristics of said coating material While in said blended and smooth surfaced distribution by subjecting said applied coating to a controlled low temperature sufficiently low to effect stabilizing of said coating material in said blended and. smoothed condition to prevent adverse adhesion between the applied coating material and the surface smoothing and blending member and maintaining said coating material stabilized in said blended and smoothed modified condition while effecting substantially complete separation of said smoothed surface and the smoothing and blending member, and thereafter treating said modified condition coating material to cause reverting from said modified condition and to effect removal of suspension liquid from the coating material and paper to reduce the liquid content to a range such as used in commercial coated papers used for printing and without objectionably effecting disturbance of said blended and smoothed surface condition to produce a finished product of predetermined surface smoothness adapted for printing, including printing such as multi-color and half-tone reproductions.

Still another object of the invention is to provide for coating paper by so applying a surfacing material such as a suspension of mineral pigment and adhesive used in the coating of so-called magazine and book paper as to give surface characteristics such as are adapted for receiving printing impressions and especially to meet highgrade printing requirements, such as half-tone and multi-color process printing and otherexacting printing such as in magazine illustrations and the like, by bringing the coated surface of the paper into contact with a surface smoothing member under such controlled and coordinated conditions of low temperature of the order of substantially below freezing and so effective upon the layer of coating that the normal adhesion of the coating material for the smoothing surface is so materially aifected that a substantially smooth surfaced and uniformly blended coating will exist upon the paper after the coating material has been brought against and then separated from the smoothing surface member.

It is also an object of the invention to provide such a process for manufacturing such a web of paper in which the coated web of paper is brought into contact for a predetermined limited period of time with a smooth surfaced heat transferring member refrigerated to predetermined low temperature conditions such that the normal tendency of the coating to adhere to such surface is altered by its refrigerating, and after such limited period of contact sufficient to cause a smoothing of and altering of the normal adhesive characteristics of the coating on the paper surface, the coated paper leaves such smoothing surface with substantially complete separation of the coating therefrom to thus provide temporary conditions effective to retain essentially the smoothed surface condition established upon the surface of the coating while in contact with such member until said separation has been completed.

It is a still further object to provide a method of manufacturing coated paper in which the coated surface of the sheet is brought into sur- 1 face smoothing contact with a substantially smooth member refrigerated to a predetermined low temperature effective upon the coating suspension within the range of substantially below freezing and such that the normal adhesive characteristics of the coating material for the smoothing memberiare modified and substantial or objectionable adhesion of the coating material to the smoothing surface is prevented, to permit removal of the modified smoothed surface of the paper coating material from the smoothing and refrigerating member without objectionable adverse eifect upon the smoothness thereof.

It is also an object to provide a process to coat a web of paper in which the coated sheet is brought into contact for a limited period of time with a smooth surfaced member which is maintained at such temperature that at least the surface zone of the coating is frozen to reduce the adhesion of the coating for the member so that the smoothed surface of the coating retains the surface smoothness characteristics imparted thereto by such surface after separation therefrom.

Another object of the invention is to provide such a method in the manufacturing of paper in which the coating upon the paper is of such constituency as to be deformable by a smoothing and modifying member to produce a substantially smooth surface in the coating applying zone and to be modified in the applying zone so that said substantially smooth surfaced coating will be retained after the coating moves away from said smoothing and modifying zone and that subsequent drying after removal from such zone will not objectionably affect the smoothness and uniformity for predetermined printing characteristics thereof and without the necessity of supercalendering of such coated product.

Still another object of the invention is to provide a method of manufacturing such paper, in which the non-aqueous constituents of the coating material include a predominant proportion of finely divided mineral pigment, and in which the coating is subjected to a smoothing and blending operation to produce a suitably smooth surfaced and blended layer or film, and is subjected sequentially to said blending and freezing of the blended and smoothed surface layer or film, the smoothness and finish characteristics of the surface being maintained to meet predetermined printing characteristics after removal of the coated paper from the freezing zone and subsequent drying and until delivered as a finished coated product.

Another object of the invention is to provide a process in the production of such coated paper, which comprises the steps of subjecting a coated traveling web having a predetermined quantity of mineral coating suspension thereon to a smoothing operation to produce a substantially smooth coating, effecting freezing of the smoothed coating and removing of such frozen smoothed coated paper from the freezing zone while substantially maintaining its smoothness and finish characteristics.

Another object is to provide apparatus for said coating of paper in which in the coatin applying zone of said apparatus means is provided for applying coating material, such as mineral suspension coating material used in the preparation of so-called magazine and book papers, in controlled quantity and distribution per unit area, and additional means is provided in said coating applying zone which additional means comprises a member for effecting a blending of the applied coating material and a surface smoothing thereof to give a substantially uniform and smooth surface distribution of the blended coating on the paper, with refrigerating means sequentially effective with relation to the smoothing and blending member and operable at predetermined low temperature, of the order of substantially less than freezing, to stabilize said blended and smooth surfaced layer of coating material to a modified condition such that the normally substantial and objectionable adhesive characteristics of the coating material with respect to the smoothing and blending member are temporarily so substantially affected that the smooth surfaced and blended coating may be removed from contact with said means to efiect substantially complete separation without adversely disturbing the smooth stabilized condition of the applied coat- It is also an object to provide apparatus for forming a smooth surface coating on a paper web in which the coated web surface is brought into contact for a limited period of time with a smooth surfaced member maintained at said low temperature conditions such that the normal tendency of the coating to adhere to the member temporarily is so materially reduced as to effectuate that the smoothed coated surface when separated from said member will substantially completely retain the surface smoothness characteristics imparted thereto by said member.

Another object of the invention is to provide apparatus effective in the coating applying and treating zone, for practicing said method or methods.

Another object of the invention is to provide a coated paper product having the coating with said blended and smooth surface characteristics and for predetermined printing characteristics after the applied coating has been caused to revert and subjected to the desired drying and without further processing thereof.

Another object is to provide a paper adapted to receive such printing surface and smoothness and finish as an applied coating and without the necessity of supercalendering.

Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings, and appended claims.

In the drawings, which illustrate apparatus embodying, and found satisfactory for practicing and effectuating, the inventions hereof- Fig. 1 is a diagrammatic view in side elevation showing apparatus constructed in accordance with and for carrying out the practicing of the present invention;

Fig. 2 is a similar view of a somewhat modified arrangement of the apparatus;

Fig. 3 is a broken sectional view, somewhat diagrammatic, of a roll found satisfactory in the carrying out and effectuating of the methods of this invention, said view corresponding substantially to the line 3-3 of Fig. 4, and indicates a way of maintaining the desired controlled low temperature within the coating applying zone;

Fig. 4 is an end elevational view of the roll shown in Fig. 3;

Fig. 5 is a further modification of the apparatus used for carrying out the practicing of the present invention; and

Fig. 6 is a diagrammatic showing of an alternate arrangement for maintaining the predetermined low temperature of the roll.

In the drawings apparatus embodying and for practicing the invention has been shown, somewhat diagrammatically, which has been satisfactorily used under commercial operating conditions for producing so-called coated book or magazine paper of such kind as widely used in the printing industry, and more particularly in the printing of the better grade magazines including half-tone and multi-color reproductions. As shown in Fig. 1. the paper web to be coated is drawn from a roll of suitable book or magazine paper base stock, and the web, I I, is led over a guide roll I2 to pass through the apparatus into the coating color applying zone. In the modification of Fig. 1 the web passes through the nip of the coating application rolls I5, l6 where the predetermined amount of coating suspension is applied thereto and distributed with sufficient uniformity over the web surface to give the desired weight of coating materia1 per unit area (generally in the book and magazine field, this unit being the weight of coating in pounds, per side of paper, per ream of 500 sheets, 25" x 38").

In the coating of such paper a normally adhesive coating material such as a suspension or colloidal solution of pigment and adhesive material in a suspension or solvent fluid is applied by such apparatus and in such manner as to give a coated web having the surface of the coating sufliciently smooth so that the irregularities therein may be reduced by supercalendering to give a final product of smoothness and finish suitable for such printing. But the present invention permits use of simple and effective apparatus to provide a mineral coating of heretofore unattained characteristics of blending and uniformity of distribution and of surface smoothing, and it has been found particularly ad.-

film applied upon the paper surface, to give'predetermined, desirable, printing characteristics. In practice it has been found that coated papers, such as so-called coated magazine or book papers, may be so produced by the present invention that the coating suspensionmay be so applied, in the coating applying zone, as to provide a coated paper having such uniformity and surface smoothing of the coating material that when dried it may be used forman y printing operations, in the field of magazines and book paper, without the supercalendering operation as long used universally in the commercial coated paper industry; and of such characteristics that the high finish of supercalendered papers as heretofore manufactured may be much more readily and easily attained along with additional surface smoothness as desired such as for the multicolor and half-tone printin as now generally practiced in the printing of better magazines and other high-quality printing reproductions as referred to. The invention herein is dis closed and illustrated as practiced and successfully used in producing such coated magazine or book paper; and as shown the apparatus is provided for such coating on the traveling web of printing paper such as magazine orbook paper, by properly controlling the conditions surrounding the applying and distribution of the desired quantity of coating materialto the traveling web and the blending and surface smoothing of the coating as the web passes through the nip of a, pair of rolls, so that as discharged to travel away from such nip, the coating on the web will have the desired distribution, blending and surface smoothness. Forthis purpose, as shown, the coating applied on the surface of the paper is subjected to smoothing and blending contact with the smoothing surface of a member such as the roll 25, such contact being maintained for a predetermined, but satisfactorily brief, limited period of time sufiicient to assure that the fluent or properly deformable coating is blended and its surface smoothed to correspond at least with the smoothness of the roll surface. Of course, cohesion of the adhesive coating'material exerts its effect and, as will hereinafter appear, the actual surface smoothnessof the. coating aseifected at this stage in the applying and treatment of the coating will be of substan: tial effect but in any event, as herein described, and as satisfactorily practiced, the coating as applied in controlled quantity and distribution, per unit area, to thetraveling web is first given a blending and smoothing action as it is cleformable or fiowable when brought against the surface. of the r011 traveling toward the nip, and being normally adhesive for the material of the roll surface zone would conform, or tend to con-. form, to the smoothness of such surface. quentially, but with the time interval so small in actual operations at high speeds of paper coating machines as used today, of the order of 600 to 900 or more feet per minute, to be almost concurrently, there is such treatment of the blended and smoothed surface coating against the roll surface that the coating, has its characteristics temporarily modified, or it is stabilized, so that the adhesive tendency which would normally be effective between the coating material and the smoothing roll surface, .to effect some adhesion with some more or less, adherence of the coating material to the roll surface at the outside of the nip, is temporarily so greatly reduced or entirely overcome that the smoothed surface coating material does not adhere to the surface of the roll or smoothing member, but the discharge side of the nip moves away from the roll with its retained stabilized or modified smoothed surface characteristics and appears to have no, or substantially no, adhesion with respect to the roll surface. That is, the surface of the blending and smoothing and stabilizing roll 25, traveling away from the nip and away from contact with the coated surface of the Web has been found to be substantially free from the coating material, and the stabilized or modified coating on the paper Web, as the coated web travels out of and away from the discharge side of the nip, has substantially retained the blended and surface smoothness imparted to it in this sequential operation and likewise there is no substantial or practically appreciable disturbance of said blended and smoothed surface coating as it separates completely from the smoothing member and moves away from said surface and away from the discharge side of the nip.

In practical operations, utilizing the invention and the apparatus illustrated, under commercial operating conditions, this temporary stabilizing or modification of the coating, sequentially following its blending and smoothing, is brought about by lowering the temperature of the smoothing member or roll surface zone through a refrigcrating action to a low temperature effective to produce the stabilizing and modification of the coating referred to. In actual practice satisfactory results have been attained, with the blending and surface smoothing action and the stabilizing and modifying action, performed during the sequential travel of the paper and its layer of coating material through the nip of a pair of rolls 25 and 26 such as illustrated, and with the roll 25, which has its surface in contact with the coating, being of smooth surfaced metal and refrigerated to an effectively low temperature of the order of substantially below freezing, where it is effective upon the coating during the Whole period from the time the coating material first is brought against the smoothing surface until the blended and smoothed surface coating is in its stabilized or modified condition is separated cleanly, without substantial disturbing effects upon the coating, at the discharge side of the nip. Very satisfactory operations, as hereinafter more fully explained in detail, have been secured utilizing such a metal roll suitably refrigerated from the inside to brin the temperature of the roll down to substantially below zero, centigrade, and very satisfactory results have been obtained in actual practice with refrigerated roll temperatures within the range of about 20 to 40 C. While the underlying theory or principle is not fully understood, nevertheless for practical purposes it appears that when white mineral pigmented coating material using modified starch or other similarly used adhesive in a water suspension and with coated materials as heretofore known and used in the commercial coating paper industry, the practicing of this invention has seemingly resulted in temporary stabilization or modification of the applied coating so that its normal adhesive characteristics with respect to the metal of the freezing roll are either completely suppressed or so greatly reduced that the blending and smoothing may be attained and the blended and smoothed surface coating then modified or stabilized, without necessary driving off of the suspension liquid, so that at the exit side of the nip the smooth surfaced coating will have a clean, or substantially completely clean, separation which is retained as the coated paper is discharged from and moves away out of the nip.

It is not now known Whether these desirable conditions are attained as a result of freezing through the entire layer of coating, but in any event it is apparent that at least the surface zone of the coating is frozen while in contact with the smoothing member, and should be in that state as it is discharged from the nip. On the other hand, in apparatus as illustrated, where there is such short time element in the sequential operations of blending and smoothing and subjecting to the lowered temperature, the temperature should be controlled and the relationships so coordinated that the blending and surface smoothing will occur before objectionable, e. g. premature, freezing of the coating has occurred. And when these adhesive coatings of the character referred to are given such treatments, in the coating applying zone and with the smoothing and blending and low temperature stabilization or modification, the treated coating does not adhere, practically, to the surface of the roll but as stated separates therefrom at the discharge side of the nip with the described surface smoothing which has been attained.

Upon raising the temperature of the coated paper, with resultant thawing or melting of the frozen coating the smoothness of the coated surface may be substantially affected, depending upon the thickness, or weight, of coating upon the paper and the percentage of solids, the suspension liquid, the materials used, etc. Apparently upon thawing, unequal strains may be caused which tend to ruffle the surface, as it were, thus giving more or less irregularity and to some greater or less extent a change in the surface smoothness as it exists when in the stabilized or modified condition.

Fig. 1 illustrates apparatus for applying the desired quantity of coating to the web which has heretofore been widely used commercially for applying relatively high solids content coating suspensions, e. g. of the order of 60 %-65% solids or more. In such mechanism the coating color is fed through a suitable supply line and by suitable means to a series of discharge pipes or nozzles, indicated diagrammatically at H, and into the nip between a pair of rolls 20 and 2! which have the direction of rotation as indicated, to correspond with the direction of travel of the paper web, 1. e. both rolls traveling downwardly and away from the point of delivery of coating color.

Roll 20 runs in contact with the application roll 16 and provides for transferring thereto a regulated quantity of uniformly distributed coating material which in turn is transferred from roll Hi to the traveling web of paper as it passes through the nip of the application rolls 15, Hi.

It has been found in wide scale commercial operations that the above described form of apparatus is very satisfactory and effective for transferring from the trough of coating material or coating color, between the rolls 2t and 2|, of accurately controlled amounts of the coating material. With high solids content coating colors of the order of as high as 65% solids or even higher, which in their normal condition are substantially non-fiowable, this apparatus,

"9 with the rolls under considerable pressures of the order of 50-200 pounds per linear inch, effects a large temporary changefrom its normal condition of non-flowability, causing it to become readily fluent and flowable so that it may be thus accurately controlled as to quantity and general distribution. The coating material passing in controlled amount through the nip of the rolls 2G-2I passes on tothe surface of the roll I6 as it travels up toward the paper past the roll 2|], to give the desired quantity of coatin material for the predetermined coat weight desired and in such condition of fiowability, whatever its solids content, that the color will be generally distributed across the surface of the roll It as it moves toward the paper II and application nip of the rolls I5, I6. In such condition of fiowability and such distribution when brought in contact with the paper web and traveling through the nip along with the paper web there will be transferred to the web a substantially uniformly distributed layer or film of coating material which is of considerable smoothness. As the coating material used in the coating paper industry, as herein referred to,

contains a substantial amount of adhesive material, such as modified starch or casein, there is enough working of the coating color both before it passes into the application nip of the rolls I5, I 6, and also within that nip, so that even said high solids content coating colors will be made sufficiently fiuid, for securing the desired accurate coat weight and generally uniform distribution of the film upon the surface of the paper web. Also, because of its flowability and the adhesive characteristics effective as between the coating color and the surface of the application roll I5, and the cohesive characterist cs of the color itself, it has always been found that there is some splitting or separation within the film of applied color as the paper Web travels out of the discharge end of the nip and sufficiently far away from the retreating surface of the applying roll It, so that internal forces of the coating material are overcome and there is a splitting or rupturing which has heretofore been found to be generally within the body of the film so that a part of the color remains on the paper and travels away from the nip with the traveling web and a part is split off or separated. and adheres to the downwardly traveling surface of the application roll I 6. While the apparatus hereabove referred to, especially using high solids content colors with greatly reduced viscosity and corresponding fiowability, has been very satisfactory in applying the desired quantity and generally uniform distribution of coating material to the paper web, and of leaving a surface which is reasonably smooth so that it may subsequently be dried and supercalendered to give the desired high finish and smoothness for high quality half-tone and multicolor reproduction in high-quality magazine and book printing, nevertheless there are surface irregularities which, though actually within small dimensional ranges, are still sufficiently great with respect to the thickness of the ink film to be printed, etc., that they impair the printing property of the. paper. However, for many satisfactory printing operations these irregularities may be smoothed out, adequately, by supercalendering. This coating applying apparatus as heretofore described and illustrated herein is one which has been satisfactorily used inlarge scale commercial operations in the manufacture of coated magazine and book paper for many years as stated above, and it has likewise been found satisfactorily usable for applying a fluent, mobile and deformable coating, of desired coat weight, and generally uniform distribution per unit area of surface of the traveling web, for practicing the present invention.

Various coating materials may be employed in practicing the present invention and as indicated by the formulations hereinafter set forth, the coating material for such magazine and book and like coated papers surfaced to receive printing, comprises generally a mineral and an adhesive in an aqueous medium. With coating color comprising clay, calcium carbonate or other similar mineral pigments and an adhesive such as modified starch or casein, in accordance with the formulations hereinafter described, normally the adhesion of the coating material to the surface of the roll I6 is such that some of the material adheres to the surface of that roll, as stated and with the surface of the layer or film of coating material upon the traveling web having the described i egu produced by the separation of the layer of coating material. Such surface irregularities are often referred to as piling and worming and resemble small and irregular hills and valleys.

As illustrated in Fig. 1, the web II with the coating applied thereto at the nip of the application rolls, and while that layer of coating is still sufficiently mobile or deformable to permit of further forming and smoothing, is carried into the nip between the rolls 25, 26. The

spacing of the nip of rolls 25, 26 with respect to the color application nip is relatively close, although such spacing may vary somewhat depending upon the speed of travel of the web, it being preferred however to locate such rolls n close proximity to the application nip in order to assure that the applied coating retains its fluent and mobile or formable character. As shown, the uncoated side of the Web first contacts roll 26, partially wrapping it, such roll 2 6 suitably being rubber covered.

Satisfactory results have been secured with a roll 26 having a surface layer of rubber material the plastometer reading of which is of the order of 5 to P. & J a suitable value being about 30 P. & J. Rolls 25 and 26 may be operated with or without pressure therebetween, the pressure in operation satisfactorily having been varied over a substantial range, for example from about 40 to pounds per lineal inch, with satisfactory results having been obtained at a pressure of about 100 pounds per lineal inch.

Roll 25 forms the smoothing and finishing member or surface and is shown as of smooth surfaced metal or other good heat transferring material, and preferably the surface has a high polish or finish. Suchroll is refrigerated so that its surface in contact with the coating on the paper is sufficiently low so that during the limited period of time that the coating is in contact with such surfacing member, the resultant temperature decrease will cause a change in the state of the coating material to stabilize or modify it so that its normal adhesive characteristics are changed so as to insure the clean, smooth surfaced, film separation described above. The temperature of the smoothing surface member should not be so low as to freeze or set or rigidify the surface of the coating before the latter has had time to be blended and formed by contact therewith, but should be low enough so that after the surface of the coating has been conformed to the surface and finish of the smoothing member, and within the limited time of contact therewith, at least the surface zone of the coating will be definitely so modified and stabilized. Under such conditions it is found that the surface layer of coating material which has been blended and has acquired a smoothness corresponding to the smoothness of the surface of the smoothing member 25, will have its adhesion characteristics so modified that its normal tendency to adhere to the surface of such member is either eliminated or very substantially lessened to such extent that at the discharge side of the nip between rolls and 26, the surface of the coating release from the surface of the member 25 and separates therefrom substantially completely and without objectionable disturbing of the smoothness of the surface layer thereof, leaving a smooth'surface thereon free of objectionable defects such as piling and worming.

It has been found in actual operations under "satisfactory commercial operating conditions that a paper Web having a mineral pigmented-water suspension-modified starch or casein adhesive coating applied thereto of any of the formulations described below, and traveling at a speed of the order of 50,6 to 650 feet per minute, will present this phenomenon of substantially complete separation from the refrigerated surface of the roll 25 where the surface of such roll is main- 'tained within a temperature range of approximately -8 "C. to 60 C., a preferred range being from 'about"20 C. to C. With rolls of the character described it will be understood that the actual width of nip between rolls 25 and 26 is 'of the order of 1% to 1 inch, depending upon relative hardness and nip pressures, and at the speed of travel of the web as referred to, it is evident that the length of time during which the coating is in contact with the refrigerated surface of the finishing member is very limited, of the order of a small fraction of a second, and under these particular conditions continues for less than one-hundredth of a second. Variation in the temperature of the refrigerated surface of the finishing member may be effected as desired in accordance with variations in the operating conditions, particularly the width of the nip, the speed of travel of the web, the characteristics of the coating composition, and the weight of the applied coating.

In the carrying out of the invention as herein described, the layer of coating material as carried into the nip of the roll 25 and 26 is sufficiently mobile or fluent and deformable so that as it is brought against and passes along with the smooth surface of the refrigerated roll .25, the piling and worming of the coating layer that is normally formed as the paper or web passes from the discharge side of rolls l5, 16, will be smoothed and the coating blended, so that the surface of the layer of coating will acquire the smoothness and finish of the refrigerated surface of the roll 25. as the coated web passes through the nip between rolls 25 and 26 there is a blending and smoothing out of the piling and worming of the coating material on the web so that the coating acquires a smoothness corresponding to the smoothness of the polished surface of the .roll 25. This smooth condition is then preserved by the low temperature treatment, substantially below the freezing point or range of the coating, with the result that the coating material is modified or stabilized in its blended and smoothed condition and loses its usual adhesive properties for the surface of roll 25. If the roll temperature is too low, or if for any reason the layer of coating is too rough, or if the coatin is allowed to contact roll 25 ahead of the pressure zone of the nip between rolls 25 and 26, the crests of the hills, so as to speak, may freeze too quickly to permit the layer of color to adjust itself to give the smooth surface and the uniformity or blending of the color within the nip which results in the substantially uniform layer of coating having the substantially smooth finished surface referred to above. Likewise, if any coating material should for any reason adhere to the surf-ace of the refrigerated roll beyond the nip, for example accidental color splashes, and if the roll temperature is controlled to be not too low, so that such material when brought against the incoming layer of color will melt or soften and be blended with the incoming color and become a part thereof before the stabilizing action, it will release also from the surface of the refrigerated roll at the nip exit as does the blended body of coating color and therefore irregularities of surface finish and smoothness will be prevented. The refrigerated roll thus tends to be self-cleaning and is thus effectively maintained in the smooth and highly polished condition.

Under normal operating conditions, the degree of wrap of the coated traveling web on the freeze roll 25, coming out of the nip between rolls 25 and '26, is not critical insofar as producing the desired uniformly smooth coating surface is concerned, provided the temperature of the roll 25 is sufficiently low to effect said stabilizing action upon the coating while the web is passing through the freeze nip zone.

As shown in Fig. 1, the traveling web having the stabilized or frozen coating material upon it, passes over a small diameter fly roll 30 which is situated in such close proximity to rolls 2'5 and 28 that the frozen coating will not have thawed until after it has passed over roll 30. If desired, use of the fly roll 38 may be eliminated by positioning rolls 25 and 26 so that the web passes through and directly out of the nip of rolls 25 and 26', as shown in Fig. 2.

As the temperature of the coating material rises, as the coated web travels away from the modifying rolls this material reverts, or thaws, from its stabilized condition; and, as stated, during this thawing period is attended by the causing of unequal strains which tend to ruffle the surface of the reverting material. However, these conditions of disturbance to surface smoothness resulting from thawing, vary according to the characteristics of the coating, the coat weight, the amount of suspension liquid present, the low temperature attained in treatment, etc.; and the magnitude of the surface irregularities resulting from thawing has been found to be substantially less, and of a materially lower order, than the magnitude of the surface defects in coating prior to such smoothing and blending action, as for example -as widely practiced using the application rolls l5, l6 and associated parts, which have given the worming or piling described above.

Such defects resulting from thawing are relatively smalland not objectionable from the standpoint of securing high grade printing results. S-o-called coated book or magazine paper has been satisfactorily made by the present invention, and commercially printed, having a coat weight of the order of 7 to 13 pounds per ream per sideand with the paper traveling from the coating applying zone of the apparatus through usual drying cylinders or rolls, and without the resultant product, dried down to the usual moisture content of conventional coated book or magazine paper, beingsubjected to a supercalendering operation. While such coated paper, as made .under the present invention, may not have the coated paper of the present invention may be supercalendered for higher gloss and surface smoothness much more readily and with much less likelihood of blackening or otherwise adversely aifecting the finished product.

The travelingweb is then surface dried as by being passed over a series of hot air pipes indicated generally by the numeral 35, which are provided with discharge nozzles or slots so that the hot air will pass in contact with the layer of coating and thaw it or cause it to revert from its stabilized condition as it passes away from the roll 30. tioned above the web for additional drying, if desired. During this period the layer of coating loses sufiicient water such that when the web comes into contact with small drier roll 31 which guides it into the first main drier drum, indicated at 38, the coating will not adhere to nor pick off on the surface of the drier drums and it can thus be carried through the series of driers without adversely affecting the surface.

The choice of color formula employed in carrying out the invention is influenced considerably by the grade of paper to be made. Moreover, the choice of color formula is also important inasmuch as it influences the operating temperature of the freeze roll 25. It has been found that the desirable temperature of roll 25 during operations is largely dependent on coat weight desired, web speed, solids content of the coating and. choiceof coating constituents. Heavy coat weights and high web speeds require a colder roll 25 for release of the stabilized film than do light coat weights and lower web speeds. Moreover, low solids content coating materials require a colder roll 25 for effecting clean release of the frozen coating film than do high solids coatings. It is therefore apparent that the combination of high solids content and high speed operation is highly satisfactory in carrying out the invention. The commonly used coating constituents for printing paper such as clay, calcium carbonate, starch, casein and soap, when in aqueous suspension may be readily modified and stabilized or frozen to condition suitable for use in accordance with this invention. Other color constituents such as for example, rosin, and polyhydric alcohols such as glycerin which have a low freezing temperature, may be used but require that thesurface of the forming member 25 be colder in order to release the frozen color film. i

The invention is usable with coatin compositions of a different solids content and is particularly desirable for use with high solids content color where apparatus is used which provides for adequately controlling the flowability and fluidity and rate of application of the coating Certain of these pipes 36 may be posicolor as initially applied to the web. Such high solids as utilized in accordance with this invention have the advantage that the low water content of such colors expedites stabilizing or freezing the coating material. A color formula which has been found to function satisfactorily in the practicing of this invention, is of the following composition, wherein the percentage by weight is taken on a bone dry basis:

Example I 12% enzyme converted corn starch 10% fine particle size calcium carbonate 7 8% fine particle size domestic clay to which is added 1% sodium hexametaphosphate 0.75% soap 0.25% sodium carbonate 1.0% sulfonated tallow.

Such color gives satisfactory results in the practicing of this invention when admixed with water to have a solids content of approximately 64.9%.

The following examples of color formulations which have likewise been used satisfactorily are set forth for the purpose of illustration, but not of limitation. The percentages by weight of these compositions it taken on a bone dry basis:

Example II 10% enzyme converted corn starch 45 barium sulphate-zinc pigment 45 fine particle size domestic clay to which is added 0.5% sodium hexametaphosphate 0.5% calcium stearate 1.0% sulfonated tallow water to provide 76.2 solids Example III 13% casein 15% calcium carbonate 60 fine particle size domestic clay 12% satin white water to provide 37.0% solids Example IV 3 caseinsuitably dissolved with alkali 8 enzyme converted corn starch 25% fine particle size calcium carbonate 64% fine particle size domestic clay to which is added 1.0% soap .water to provide 49.3% solids Also it has been found desirable to reduce the air content of the coating color to avoid bubble formation. 7

By virtue of this invention, widely varying rawstocks may be used for meeting different demands. The rawstocks should have a smoothness con-v sistent with the coat weight to be applied and the invention permits satisfactory coating of rawstocks without the heretofore practiced control of the liquid absorbency of such rawstocks. Rawstock satisfactorily employed with the apparatus shown in Fig. 1 consisted of:

35% bleached sulfite 25% soda pulp 20 reclaimed paper or old paper 20% broke in kind 1% bentonite (filler) pound beater, was made at a speed of 596 linear feet per minute and was subjected to the treatment of the patent to Van de Carr No. 2,378,113, using five nips of the calender.

The formed paper web had a basis weight of 30 pounds per ream, moisture content of 8.1%, filler content -'of 8.6%, Mullen test of 13.5, tear test (Elmendorf) of 20.5 and finish (Ingersol) of 27.

Another arrangement for practicing the present invention is shown diagrammatically in Fig. in which the supply of coating color 60 is delivered into the nip of a pair of rolls BI, 62 by means of which a regulated quantity and substantially uniform distribution of the coating material is passed onto the surface of roll 62. Roll 62 likewise serves as an application roll, running in contact with the web of paper 63 supplied from roll 66 and passing through an application nip formed by roll 62 and a cooperating roll 66. After the coating layer is so applied the web 63 is carried by the cooperating roll 66 into the nip formed between that roll and a refrigerated roll 65 which is of the type described above in connection with roll 25. That is, it is provided with a smooth finished surface, preferably of highly polished metal, and such surface is refrigerated by suitable means to operate in the manner already described.

After leaving the nip formed by rolls 68 and 65, the web is then led around guide rolls 6B, 69, which contact the uncoated side of the web while allowing the coating to be dried by suitable air driers, or otherwise, until such time as it can be led to a wind-up roll 70 as a finished and substantially complete dried sheet of paper. If desired, this paper may be 'supercalendered to give higher finish.

Instead of providing a refrigerated roll which is cooled by a refrigerant such as solid carbon dioxide, such as Dry Ice, or the like, a continuously circulating refrigerant may be supplied to the roll, such arrangement being diagrammatically illustrated in Fig. 6. As there shown, the refrigerated roll is indicated at 86, the shaft of the roll at one end having an open passage 8| through which there extends a refrigerant supply line 82. A series of nozzles or apertures 83 are provided in the supply line within the hollow interior of the roll to provide for the supplying of the refrigerant fluid into direct contact with the inner surface of the roll. Such fluid then collects and flows out through the opened end Bl of the roll and is picked up in a trough 84, from which it is supplied to a refrigerating unit indicated generally at 86 by means of a pump 85 where it is refrigerated to the desired low temperature point for redelivery to the supply line 82. The refrigerant may be brine or other suitable liquid which has the proper physical characteristics for use as a heat transferring medium.

The. cooling or refrigerating of the smoothing and" finishing member 25' may be conveniently accomplished by the use of a smooth surfaced roll in which a refrigerant is placed, such as solid carbon dioxide, such as Dry Ice, together with a suitable liquid for transferring and distributing the low temperature effectively throughout the entire roll surface. This is illustrated in Fig. 3 in which the cylindrical roll is indicated at 40 having recessed ends to receive end members 42 which are bolted in place therein by means of bolts 43, suitable clearance being provided around the bolts to avoid the production of deforming stresses under the wide temperature changes to which the roll is subjected when operating and when at room temperature.

The roll ends receive the central supporting shaft which is bored with a longitudinal bore 46 extending out through one end thereof and with one or more cross passages 41 intersecting therewith to provide continuous communication between the interior of the roll and the outside atmosphere. A cylindrical cover 43 is secured to the end 42 and extends inwardly of the roll overlying the openings of the passages 4'! to prevent the blocking of those passages by solid particles of the refrigerant, thereby maintaining communication with the outside atmosphere and avoiding the development of excessive internal pressure.

The roll end 42 has a filling opening which is closed by a suitable plug 5|, such opening being of suflicient size to provide for the ready charging of the refrigerant into the interior of the roll. The roll end is also provided with a safety release in the form of discharge aperture normally closed by a frangible diaphragm 56 of metal or other suitable material adapted to rupture in the event that the pressure within the roll should develop to any dangerous degree, such as might occur if the passage 46 should become clogged. A protective wire screen 5! is positioned inwardly of the diaphragm 56 and prevents damaging contact of the refrigerant therewith, thus maintaining the diaphragm in condition where it is ready for operation if required. Preferably the same construction is used at both ends of the roll.

In the operation of such refrigerated roll, the roll is turned to bring the filling opening above the central line, and the hollow interior of the roll is then charged with a quantity of solid car-- bon dioxide and a liquid heat transferring medium in an amount sufiicient to bring the level of the liquid somewhat below the center line of the shaft, as indicated. The filler plug is then replaced and the roll is ready for operation, the gases released bythe sublimation of the solid carbon dioxide being continuousl discharged through passages 41 and as so that the pressure within the roll is normally maintained at atmospheric.

A mixture of denatured alcohol and carbon tetrachloride has been successfully used as a heat transfer medium in the roll 25. Alternatively a mixture of acetone and water may be used. The ratio of denatured alcohol to carbon tetrachloride, or of acetone to water represents an effective adjustment of freeze roll temperature, Increasing. the amount of denatured alcohol. relative: to the carbon tetrachloride or of acetone relative to water provides a colder freeze roll temperature, While suchadjustment of the transfer medium in the roll 25 represents an effective means for adjusting freeze roll temperature, variations in. the quantity of solid carbon dioxide introduced into the roll interior also have an effect on. the temperature of this roll. Based on commercial operations, however, it has been foundv that roll temperature may be more satisfactorily adjusted through proper choice of the heat transfer mixture than by large variation in the amount of frozen carbon dioxide carried in the roll.

For example, with a roll 16 inches in diameter, using two parts of denatured alcohol and one part of carbon tetrachloride and approximately pounds of Dry Ice for each three feet of roll length,th'e roll being just under half filled, resulted in a temperature of about 40 C., but

when using equal proportions of alcohol and carbon tetrachloride and the other conditions as stated above, the temperature was of the order of 25 C. to 30 C.temperatures attained being affected by the tendency of the solid carbon dioxide to more or less freeze the liquid in the roll according to the rate of heat transfer in operation.

The apparatus as shown somewhat diagrame matically in Figs. 1 and illustrate, somewhat conventionally, the practicing of the invention in coating a web of paper, drawn from a roll, carried by suitable reel or the like, as is well understood. However, the paper to be coated may come from another supply source, Fig. 2 for example showing in diagrammatic form a paper machine which would comprise the usual forming wire, suitable driers, etc., and is illustrative of so-called machine coating in which the coating apparatus is located in line with the paper, machine so that the formed web may travel through the coating mechanism and the making of the paper web and its coating performed as one continuous manufacturing operation. The driers, and other parts of the usual paper machine are not specifically shown, but can be of usual construction. All of the drier drums following the coating mechanism are not illustrated, as the proper number of drier drums will be used according to understood practices.

And-whether a machine coating mechanism, or having the paper passed to the coating apparatus from some other source, is employed, the mechanism for applying the desired amount of coating material to the Web prior to the described treatment of the coated web at the low temperature modifying and stabilizing zone is generally referred to herein as the coating applying zone of the equipment.

The modifying and stabilizing rolls 25, 26 and 25', 26-, and 65, 66 are spaced a suitable distance from the part of the apparatus which applies the coating material such as the rolls l5, l6, so that the coating material will be in proper quantity and so distributed upon the paper that it willbe within the smoothing and blending capacity of the rolls at the low temperature zone. Very satisfactory results have been attained in the making of commercial coated paper using the apparatus illustrated, e. g., in Fig. 1 of the drawings, where the nip of the rolls 25, 26 is approximately three feet from the discharge of the nip between the application rolls I5, l6,

whereas in the modification illustrated in Fig. 5 the distance'from the application nip to the cold hip is approximately a fourth of the circumference of the roll 66, which in the actual mechanism illustrated gives a distance of approximately twelve inches. Also the'coatinginateri'al may be satisfactorily applied in quantity and in distribution across the web by mechanisms other than the color application apparatus illustrated in Figs. 1 and 2 for example, which however have been found to function very satis-j factorily in actual operations as 'stated 'above'.'

For example, the coating material may be ap'-' plied in suitably controlled quantityand ade quately distributed over the web by utilizing the color applying roll mechanism of patent to Traquair 1,597,219.

In addition, it has been found important for" securing satisfactory results that the coldroll" 25' shall be clear of objectionable ice at the time of starting andalso 'durin'g the'carrying on of the f v I v 75 While'the methods and forms of apparatus practicing of this invention! For example,

18 when the coating operation is started up a substantial time factor may be involved in reducing the temperature of the rolls 25, 25' and to the desired low temperature, within the range referred to above, for satisfactory practicing of the invention, and during this period it has been found that ice may be formed to adhere to the roll 25, as its temperature is being lowered as desired, and such ice can prevent satisfactory starting of operations and the presence of such objectionable ice would interfere with proper operation of the process at whatever time it may occur objectionably during the coating operations.

.If the roll 25 is exposed to the air in the absence of the passage of a web thereover, e. g., when not rotating or rotating without the coated web passing thereagainst, as in starting periods, the roll surface tends to condense moisture from the air surrounding it which, within the zone of the roll from the discharge side of the nip around to the inlet side thereof, may freeze as a thin film of ice. The existence of a film of ice on the freeze roll is somewhat detrimental during operation in that certain coating materials do not readily release from such a surface. However, it has been discovered that if operations are started before an ice film forms or after a thin film of low freezing point liquid such as butyl alcohol has been applied to the outer surface of roll 25 to remove the ice film, the passage of the web removes substantially all the moisture which may thereafter condense as frost on the roll.

In practicing the invention under normal operating conditions, it has been found that a frost film, as distinguished from an ice film, forms about the freeze roll 25 which film, however, has been found to be substantially or completely free of mineral material. As pointed out above, an ice film is detrimental to release of the coating material from the surface of roll 25. In contradistinction, the presence of a frost film has been found not to be detrimental to such release. While a, frost film may be continually deposited on the surface of roll 25, such film reaches a state of equilibrium and does not increase in thickness during operation inasmuch as the traveling web removes the frost as it is formed, Such removal of frost by the web is believedto be analogous to the removal of coating color as described above in connection with the. self-cleaning phenomenon. Even though roll ZSf'during operations using the form of equilibrium frost film, it has been found that the conditions described will produce such a smooth.

finished'surface upon the layer of coating leaving the nip of the rolls 25 and 26 that when subsequently dried and subjected to ordinary m'ac'hine'calendering, the final coated paper web will ha've a'surface which is adequately smooth ando-f' such finish characteristics as to provide for print ing'fas' referred to above.

Ina'ddition to applying a very superior coating tdblookbnmagazin e paper as described above, this'"invention likewise has been used satisfactorilyfor"applying superior coatings to other base sheets, such for example as paperboard (lined and unli-ned) light weight sulphite waxing papei, machine'finished book rawstock, groundwoo'djcoating rawstock (machine-finished and supered' finishes), glassine, rosin-sized cofie'e bag stock and cellulose acetate.

herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In the coating of paper to provide a substantially smooth and finished coating surface for receiving printing and the like, the method which comprises the steps of applying and distributing a predetermined and metered quantity of fluent mineral coating suspension to form a surface coating on the paper, bringing the coated surface of said paper into surface deforming contact with a movable smoothing member while said coating is still fluent and deformable on said paper to produce a substantially uniform and smooth surfaced layer of coating, concurrently effecting freezin of at least the surface zone of said coating while said coating is in contact with said smoothing member, and removing said paper and frozen coating from said smoothing member while substantially maintaining the smoothness of said frozen coating surface.

2. In the coating of paper to provide a substantially smooth and finished coating surface for receiving printing and the like, the method which comprises the steps of applyin a coating of fluent mineral coating material to a sheet of paper, subjecting said coating material on said sheet to contact with a smoothing and freezing member to produce a substantially smooth surfaced layer of frozen coating on said paper sheet, removing said paper sheet and frozen coating from said smoothing and freezing member, and effecting thawing and drying of said coating material on said paper sheet.

3. In the manufacture of coated paper having a smooth and highly finished surface for receiving printing and the like, the steps comprising applying an aqueous mineral-adhesive coating suspension of approximately 35% to 76% solids content to the paper in an initially fluent and deformable condition to form a coating thereon, contacting said coated surface While still fluent and deformable with a smoothing member for a limited period of time sufficient to form a smooth surface thereon, simultaneously stabilizing said coating against adhesion to the surface of said member by lowering the temperature of said surfacing member substantially below the freezing point of said aqueous medium, and thereafter withdrawing said paper from said surfacing member with substantially complete separation of the coating therefrom.

4. In the manufacture of coated paper having a smooth and highly finished surface for receiving printing and the like, the steps comprising applying a uniformly distributed layer of aqueous coating suspension to the paper in an initially fluent and deformable condition, contacting said coating layer while still fluent and deformable with a movable smoothing member for a limited period of time sufficient to cause blending and to form a smooth coated surface thereon, freezing the surface of said coating while in contact with said member and moving therewith to lower its adhesion for said smoothing member to a value below the internal cohesion of the coating layer itself, and separating said coated surface from said smoothing member with substantially complete retention of the coating upon said paper.

5. In the coating of paper with an aqueous suspension of mineral coating color, the steps which comprise smoothing the surface of the coating while still mobile and fluent and deformable on the paper by direct contact solely with a smoothing member maintained at a temperature below freezing to stabilize at least the surface zone of said coating, separating said coating on said paper from said member while so stabilized, and thereafter drying said coating.

6. In the coating of paper to produce surface characteristics adapted for receiving printing and the like, the method of forming a smooth surface on a layer of aqueous coating composition applied to paper which comprises the steps of subjecting said applied coating on said paper while the coating is still fluent to surface deforming contact with a smooth surfaced smoothing member maintained at a temperature below freezing for subjecting the coated surface of said paper to direct surface smoothing action and for reducing the temperature of said coating to stabilize it against adhesion to said member, and thereafter separating said coating from said member with substantially complete retention of all said coatin on said paper.

7. In the coating of paper to produce surface characteristics adapted for receiving printing and the like, the method of forming a smooth surface on a layer of fluid coating composition applied to paper which comprises the steps of smoothing the surface of said applied coating with a smoothing member maintained at a temperature substantially below the freezing point of said coating for stabilizing said coating against adhesion to said member to provide substantially complete release of 'said smoothed coating from said member, thereafter separating said paper and applied coating from said member, and drying said coating on said paper.

8. In the coating of paper to produce surface characteristics adapted for receiving printing and the like, the method of forming a smooth surface on a layer of aqueous coating composition applied to paper which comprises the steps of smoothing the surface of said applied coating with a smooth member maintained at a temperature of the order of 8 C. to -60 C. for freezing at least the surface zone of said coating to prevent adhesion to said member, thereafter separating said paper and applied coating from said member while the surface remains frozen to effect substantially complete retention of said coating on said paper, and thawing and drying said coating on said paper.

9. In the coating of paper to produce surface characteristics adapted for receiving printing and the like, the method of forming a smooth surface on a layer of aqueous coating composition applied to paper which comprises the steps of passing said applied coating on said paper while said coating is still mobile and fluent into surface deforming contact with a smoothing member, maintaining said smoothing member at a temperature substantially below freezing for immobilizing said coating in smoothed surface condition to provide substantially complete release of said coating from said smoothing member without adhesion thereto, separating said smoothed and immobilized coating on said paper from said smoothing member, and thereafter effecting thawing and drying of said applied coating while maintaining said smoothed surface characteristics.

10. The method of coating paper to provide a substantially smooth coated surface adapted for receiving printing and the like which comprises the steps of applying an aqueous mineral coating composition in uniformly distributed and metered amount to the paper, subjecting said applied coating on said paper while still fluent and deformable to surface smoothing contact with a smoothing member maintained at a temperature substantially below freezing for blending and smoothing the surface of said applied coating on said paper and for reducing the temperature of said coating to stabilize it against adhesion to said member, separating said paper with said stabilized coating thereon from said member with substantially complete release of all said coating from said member, and thereafter drying said coating while maintaining said smooth surface thereon.

11. Apparatus for the continuous coating of a web of paper to provide a smooth surface for receiving printing and the like, which comprises in combination means for advancing a continuous web of paper to be coated along a predetermined path through said apparatus, coating application means in said path for applying to said advancing web a uniformly distributed layer of coating composition, a smoothing member positioned in said path for contacting said web subsequent to said coating applying means, said smoothing member being immediately adjacent said coating applying means, means for bringing the coated surface of said web into surface deforming contact with said smoothing member while the coating thereon is still mobile and deformable, refrigerating means for maintaining the surface of said smoothing member at a temperature below freezing for stabilizing said coating to prevent adhesion thereof to the surface of said smoothing member, air drying means effective upon the coated surface of said web after leaving said smoothing member, and drum drier means for drying said coating on said Web to produce said smooth surface coated paper.

12. In apparatus for the continuous coating of a web of paper to provide a smooth surface for receiving printing and the like and having means for advancing a web of paper to be coated and coating applying means for applying to said advancing web a uniformly distributed layer of coating composition, the combination of a rotatable smoothing member adjacent said coating applying means, said rotatable member having a substantially smooth surface for contacting the surface of coating applied to said web while said coating is still mobile and deformable, pressure means for urging the coated surface of said web against said smoothing member with substantial pressure for blending and smoothing said coating on said web and imparting to said coating said smooth surface characteristics of said member, and refrigerating means for maintaining the surface of said smoothing member at a temperature substantially below freezing for stabilizing said coating against adhesion thereof to said surface of said smoothing member, means for withdrawing said web with said stabilized coating thereon from said smoothing member without disruption of smooth surface characteristics imparted to said coating by said member, and means for supporting said coated web free from surface deforming contact for a substantial distance after leaving said smoothing member.

13. In apparatus for the continuous coating of a web of paper having means for advancing a web of paper to be coated, means for applying a fluid coating composition to said advancing web and means for drying said applied coating on said web, the combination of a smoothing roll having a substantially smooth surface, said roll being immediately adjacent said coating applying means for contacting coating applied to said Web while said coating is still mobile and deformable, resilient pressure means cooperating with said smoothing roll for urging said coating surface against said smoothing roll to impart the substantially smooth characteristics of the surface of said smoothing member, refrigerating means for maintaining said smooth surface of said smoothing roll for urging said coated surtially below the freezing point of said coating to stabilize said coating in contact with said smoothing roll preventing adhesion thereof to said surface and providing for substantially complete release of said coated web from said smoothing roll with retention of substantially all said coating on said web, means for supporting said coated web for a substantial distance after leaving said smoothing roll and before the coated surface of said web contacts said drying means, and means for heating said stabilized coated to effect reversion of said coating substantially to its condition prior to said stabilizing without disruption of smooth surface characteristics imparted by said smoothing roll.

14. As a new product of manufacture, a coated paper having a surface layer of mineral pigmented coating of extreme smoothness adapted for receiving fine printing, the external surface of said coating layer being characterized in the absence of supercalendering by extreme smoothness and the absence of film split patterns characteristic of roll coated papers prior to supercalendering, and said surface of said coating being further characterized by having been produced in accordance with the method of claim 6.

RUDOLPH N. GRIESHEIMER. ROBERT C. HYDELL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re.17,854 Kratz Nov. 4, 1930 1,892,484 Dixon Dec. 27, 1932 1,997,984 Swan Apr. 16, 1935 2,304,818 Grupe Dec. 15, 1942 2,331,922 Montgomery Oct. 19, 1943 2,405,977 Peters Aug. 20, 1946 2,451,597 Wheeler Oct. 19, 1948 

1. IN THE COATING OF PAPER TO PROVIDE A SUBSTANTIALLY SMOOTH AND FINISHED COATING SURFACE FOR RECEIVING PRINTING AND THE LIKE, THE METHOD WHICH COMPRISES THE STEPS OF APPLYING AND DISTRIBUTING A PREDETERMINED AND METERED QUANTITY OF FLUENT MINERAL COATING SUSPENSION TO FORM A SURFACE COATING ON THE PAPER, BRINGING THE COATED SURFACE OF SAID PAPER INTO SURFACE DEFORMING CONTACT WITH A MOVABLE SMOOTHING MEMBER WHILE SAID COATING IS STILL FLUENT AND DEFORMABLE ON SAID PAPER TO PRODUCE A SUBSTANTIALLY UNIFORM AND SMOOTH SURFACED LAYER OF COATING, CONCURRENTLY EFFECTING FREEZING OF AT LEAST THE SURFACE ZONE OF SAID COATING WHILE SAID COATING IS IN CONTACT WITH SAID SMOOTHING MEMBER, AND REMOVING SAID PAPER AND FROZEN COATING FROM SAID SMOOTHING MEMBER WHILE SUBSTANTIALLY MAINTAINING THE SMOOTHNESS OF SAID FROZEN COATING SURFACE. 